1. Field of the Invention
The present invention relates generally to papermaking, and relates more specifically to fabrics employed in making press felts on a paper machine, pulp machine fiber cement belts, and corrugated paper board, or box-board. The invention also relates to the monofilament base of fabric optionally with a needled batt which can provide one or more of the following advantages: hydrolysis resistant materials, providing light weight high strength fabrics, having a high permeability, and soft surface with a high coefficient of friction. The present invention also relates to an integrated loop seam integrated with machine direction yarns of the monofilament base which can provide one or more of the following advantages: extremely stable and flexible corrugator fabric, and the ability to provide a non-marking loop seam.
2. Discussion of Background Information
On corrugator box-board machine, there is a transformation from sheets of linerboard paper and corrugating medium paper into corrugated box-board. This is achieved by the application of a liquid adhesive to the three sheets of paper and the pressing by one or more corrugator belts, woven or needled or a combination thereof, onto a series of steam heated plates to dry the adhesive, thereby “gluing” the paper assembly together. The heat from the plates is conducted directly to the “glued paper” (corrugated boxboard) and through this into the corrugator belt. As well as this drying function, the belt must pass the corrugator boxboard through the cooling section and onto the next stage. Frictional forces between the corrugator belt, specifically the face, or boardside thereof, and the corrugated paper board are primarily responsible for pulling the latter through the machine.
During the papermaking process, a cellulosic fibrous web is formed by depositing a fibrous slurry, that is, an aqueous dispersion of cellulose fibers, onto a moving forming fabric in the forming section of a paper machine. A large amount of water is drained from the slurry through the forming fabric, leaving the cellulosic fibrous web on the surface of the forming fabric.
The newly formed cellulosic fibrous web proceeds from the forming section to a press section, which includes a series of press nips. The cellulosic fibrous web passes through the press nips supported by a press fabric, or, as is often the case, between two such press fabrics. In the press nips, the cellulosic fibrous web is subjected to compressive forces which squeeze water therefrom, and which adhere the cellulosic fibers in the web to one another to turn the cellulosic fibrous web into a paper sheet. The water is accepted by the press fabric or fabrics and, ideally, does not return to the paper sheet.
The paper sheet finally proceeds to a dryer section, which includes at least one series of rotatable dryer drums or cylinders, which are internally heated by steam. The newly formed paper sheet is directed in a serpentine path sequentially around each in the series of drums by a dryer fabric, which holds the paper sheet closely against the surfaces of the drums. The heated drums reduce the water content of the paper sheet to a desirable level through evaporation. It should be appreciated that the forming, press and dryer fabrics all take the form of endless loops on the paper machine and function in the manner of conveyors. It should further be appreciated that paper manufacture is a continuous process which proceeds at considerable speeds. That is to say, the fibrous slurry is continuously deposited onto the forming fabric in the forming section, while a newly manufactured paper sheet is continuously wound onto rolls after it exits from the dryer section.
Contemporary fabrics are produced in a wide variety of styles designed to meet the requirements of the paper machines on which they are installed for the paper grades being manufactured. Generally, they comprise a woven or other type base fabric. Additionally, as in the case of fabrics used in the press section, the press fabrics have one or more base fabrics into which has been needled a batt of fine, nonwoven fibrous material. The base fabrics may be woven from monofilament, plied monofilament, multifilament or plied multifilament yarns, and may be single-layered, multi-layered or laminated. The yarns are typically extruded from any one of the synthetic polymeric resins, such as polyamide and polyester resins, used for this purpose by those of ordinary skill in the paper machine clothing arts.
The woven base fabrics themselves take many different forms. For example, they may be woven endless, or flat woven and subsequently rendered into endless form with a woven seam. Alternatively, they may be produced by a process commonly known as modified endless weaving, wherein the widthwise edges of the base fabric are provided with seamin loops using the machine-direction (MD) yarns thereof In this process, the MD yarns weave continuously back-and-forth between the widthwise edges of the fabric, at each edge turning back and forming a seaming loop. A base fabric produced in this fashion is placed into endless form during installation on a paper machine, and for this reason is referred to as an on-machine-seamable fabric. To place such a fabric into endless form, the two widthwise edges are brought together, the seaming loops at the two edges are interdigitated with one another, and a seaming pin or pintle is directed through the passage formed by the interdigitated seaming loops.
Further, the woven base fabrics may be laminated by placing at least one base fabric within the endless loop formed by another, and by needling a staple fiber batt through these base fabrics to join them to one another as in the case of press fabrics. One or more of these woven base fabrics may be of the on-machine-seamable type. This is now a well known laminated press fabric with a multiple base support structure.
In any event, the fabrics are in the form of endless loops, or are seamable into such forms, having a specific length, measured longitudinally therearound, and a specific width, measured transversely thereacross.
Reference is now made more specifically to industrial fabrics used in the manufacture of corrugated paper board, or box-board, on corrugator machines. Such an industrial fabric is used to form corrugator belts. On corrugator machines, corrugator belts support and pull a sheet of liner board and a sheet of paper board which pass over a roll which adds flutes or CD corrugations to the paperboard sheet. Then these at least two paperboard sheets supported by one or more belts are passed first through a heating zone, where an adhesive used to bond the at least two layers of the board together is dried and cured, and then through a cooling zone. Frictional forces between the corrugator belt, specifically the face, or board, side thereof, and the corrugated paper board are primarily responsible for pulling the latter through the machine.
Corrugator belts should be strong and durable, and should have good dimensional stability under the conditions of tension and high temperature encountered on the machine. The belts must also be comparatively flexible in the longitudinal, or machine, direction, while having sufficient rigidity in the cross-machine direction to enable them to be guided around their endless paths. Traditionally, it has also been desirable for the belts to have porosities sufficient to permit vapor to pass freely therethrough, while being sufficiently incompatible with moisture to avoid the adsorption of condensed vapor which might rewet the surfaces of the corrugated paper product.
As implied in the preceding paragraph, a corrugator belt takes the form of an endless loop when installed on a corrugator machine. In such form, the corrugator belt has a face, or boardside, which is the outside of the endless loop, and a machine side, which is the inside of the endless loop. Frictional forces between the machine side of the belt and the drive rolls of the corrugator machine move the corrugator belt, while frictional forces between the faceside and the sheet of corrugated board pull the sheet through the machine.
Corrugator belts are generally flat-woven, multi-layered fabrics, each of which is woven to size or trimmed in the lengthwise and widthwise directions to a length and width appropriate for the corrugator machine on which it is to be installed. The ends of the fabrics are provided with seaming means, so that they may be joined to one another with a pin, pintle, or cable when the corrugator belt is being installed on a corrugator machine.
On corrugator box-board machines, there is a transformation from sheets of linerboard paper and corrugating medium paper into corrugated box-board. This is achieved by the application of a liquid adhesive to the three sheets of paper and the pressing by one or more corrugator belts, woven or needled or a combination thereof onto a heating zone. In a typical corrugator machine, the heating zone comprises a series of steam-heated plates to dry the adhesive thereby “gluing” the paper assembly together, and the sheet of corrugated board is pulled by the corrugator belt. A plurality of weighted rollers within the endless loop formed by the corrugator belt press the corrugator belt toward the hot plates, so that the corrugator belt may pull the sheet across the hot plates under a selected amount of pressure. The weighted rollers ensure that the sheet will be firmly pressed against the hot plates, and that frictional forces between the corrugator belt and the sheet will be sufficiently large to enable the belt to pull the sheet. As well as this drying function, the belt must pass the corrugated box-board through the cooling section and onto the next stage.
In view of the description noted above, corrugator belts must possess certain features such as strength, durability, be dimensionally stable, and have a non-marking seam under all the conditions of high temperature steam, plus high tension. Furthermore, the belts should be flexible in the machine direction yet be sufficiently stable in the cross machine direction so as to maintain close to the belt's original dimensions and facilitate the ability to be guided along its passage around the machine under the conditions described. More importantly, the belts should be sufficiently permeable to allow the evaporation of vapor to pass easily through the material so as not to rewet the corrugated box-board.
However, corrugator belts exhibiting all of the above desirable features have heretofore not been available. Conventional corrugator belts exhibited low permeability and used the principle of adsorption and then evaporation but problems of rewetting the corrugated box-board occurred which means the corrugator machine was restricted to speed because drying was being restricted. Moreover, these types of belts were typically heavy and very low in permeability.